A ball-screw drive is composed of a spindle, a nut with a ball return, and balls as rolling elements. It is used to convert rotation into a linear motion, that is torque into thrust, or vice versa. For example, in a steering system the threaded spindle converts the rotation of an electric motor with high precision into a linear displacement of the threaded spindle, the smallest paths thus being easily and safely adjustable. The balls in a drive connect the spindle and the nut, rolling in raceways of the nut. The geometrical accuracy of the raceway and its surface quality have an effect on the smooth running and precision with which the adjusting movements can be carried out.
Different designs of nuts are known, differing primarily based on the type of ball return. The ball return can be a separate ball-circulation tube extending outside the nut. Nuts are also known with integrated ball return formed by passages or recesses on their inner surface forming a path for ball return.
From DE 103 33 909 a multipart nut is known having raceways and tracks for ball returns. The raceways formed by cold working are finished by grinding. The shape accuracy and the surface quality of the machined raceways have an effect on the service life of the ball-screw drive and the smooth running of the ball-screw drive. Waviness cannot be eliminated by grinding the raceway. In the case of very high requirement, for example in steering systems, ground raceways cannot yet fully meet requirements.